This invention relates to printing of both text and non-text (graphics) material in printing apparatus employing an array of sources of media marking elements, such as ink jets, and particularly to the activation of the marking elements to optimize the quality of printed text and printed non-text material.
Various types of printing devices are known for printing markings on a print medium. Of particular interest herein is a printing device employing a linear array of printing elements constituting a printhead which moves along the medium in a direction perpendicular to the linear array. In one well-known form of such printing device, two printheads are joined together in a unitary print-head assembly wherein one of the linear arrays comprises color marking elements, such as inkjets, while the second linear array comprises black marking elements, such as inkjets. For example, the first printhead may comprise a linear array of inkjets wherein some of the inkjets employ yellow ink, some of the inkjets employ magenta ink, and the remainder of the inkjets employ cyan ink. In the second printhead, all of the inkjets employ black ink. In a typical printing task, both of the printheads may be employed in presenting a graphic subject such as scenery having multiple colors and black, while only the second printhead is employed for printing black text within the subject imprinted on the medium.
In one typical form of construction of the color printhead, the inkjets are grouped together by color. For example, the inkjets may be arranged in a yellow band, a magenta band, and a cyan band. In order to provide an interleaving of the swaths of color laid down on the medium during successive passes of the printhead assembly across the medium, it is common practice to advance the medium, transversely to the direction of head movement, by a distance of one-half the width of a color swath for improved print quality. This has been found to minimize the effect of possible variations in the spraying patterns of successive ones of the color inkjets. Also, it has also been the practice, in the operation of a printhead, to employ some form of randomizing in the activation of the various ones of the inkjets during successive ones of the passes of the printhead assembly so as to obtain improved uniformity in the printing of regions of the subject matter.
In the foregoing technique for interleaving the swaths of color laid down by the inkjets in a printhead, a problem arises in that this technique introduces a lack of clarity in lettering or text wherein the edge lines of each printed character are not as sharply defined as is desirable.
The aforementioned problem is overcome and other advantages are provided, in accordance with the practice of the invention, by implementation of a printing mode wherein the printing of text is separated from the printing of non-text material. To facilitate description of the invention, in accordance with a first embodiment of the invention, it is presumed that the text is printed with black ink by a single print head (the black printhead) while the non-textual material may include both color and black, wherein the color is printed by use of a separate printhead (the color printhead) having inkjets operative with magenta, yellow and cyan inks. A single printhead assembly carries both printheads. The black text, in a region of the medium, is printed solely within a single pass of a printhead laying down solely black ink across the region of the medium while more than one pass is provided for the color printhead to lay down colored inks in the same region of the medium. The printing of the black text is accomplished independently of the interleaving and randomizing of the various colors and black components of the non-textual subject matter.
As a matter of convenience in the implementation of the invention, the black textual material may be imprinted simultaneously with the printing of black non-textual material subject to the proviso that while a plurality of passes of the printhead assembly may be employed for printing black markings over a band of subject matter equal in width to the length of the black inkjet array, only one pass of the plurality of passes of the printhead assembly is employed for the printing of the textual material. Thereby, the printing of the textual material is free from the foregoing interleaving and randomizing procedures for the printing of non-textual subject matter such as scenery on the medium. As a result, the textual material is provided with clearly shaped characters, such as alphanumeric characters, these characters being superposed upon the graphical, non-textual, portions of the subject matter.
If the text were to be printed in a color such as magenta, by way of example, rather than in black, then, in accordance with the first embodiment of the invention, a separate printhead would be used for the magenta rather than for the black. Alternatively, in accordance with a second embodiment of the invention, the principle of printing the text in a single pass of the printhead is applied to the color printhead such that, in the foregoing example of magenta, non-textual or graphic material would be printed in more than one pass of the color printhead across a region of the medium while the textual material would be printed solely within a single pass of the color printhead across that region of the medium.
In a further feature of the invention, there is examination of binary digital pixel signals that are fed to the inkjets to produce the image on the medium. These pixel signals are one bit signals that serve as print command signals for directing the respective inkjets to print a mark or to leave a blank space on the medium. As a result of the examination of the pixel signals, the printing protocol may be altered, based on the presence or absence of color or black. This is accomplished efficiently by concurrent examination of print command signals of individual ones of a plurality of color and black signals by use of an OR function to search for a color or black print command signal. Such information may be used to speed up the printing process by deleting extra passes of the printhead assembly employed for the foregoing interleaving in the situation, wherein only one of the foregoing colors is to be employed.
In the ensuing description, the principles of the invention will be described first with respect to the first embodiment of the invention, with a printing of text in black ink.